1. Field of the Invention
The present invention relates to an apparatus for measuring mercury contained in the gaseous medium for measuring the quantity of mercury contained in exhaust gases emitted from a chemical plant such as, for example, fossil fuel burning facilities, waste incinerators or chemical processes and, more particularly, to an automatic cleaning of the apparatus for measuring the quantity of mercury contained in a gaseous medium.
2. Description of the Prior Art
Mercury contained in various exhaust gases emitted from a chemical plant such as, for example, fossil fuel burning facilities, waste incinerators and chemical processes is generally found in two chemical forms; zerovalent mercury (Hg0) such as metal mercury, and divalent mercury (Hg2+). Of them, the metal mercury is difficult to dissolve in water and is apt to diffuse into the atmosphere, constituting a cause of atmospheric pollution. On the other hand, the divalent mercury is easy to dissolve in water and does often constitute a cause of soil contamination.
As discussed above, metal mercury and divalent mercury contained in the exhaust gases brings adverse influence on the environment and, therefore, the apparatus for measuring mercury contained in the gaseous medium is disposed in, for example, a wall defining a flue (or pipe) of the burning facilities and chemical plants so that the quantity of mercury contained in the exhaust gases can be monitored at all times.
The apparatus for measuring mercury contained in the gaseous medium referred to above includes a gas introducing passage fluid connected in parallel to the flue and is connected, in the order from the flue in a downstream direction, with a reducing tube (reducing column) filled with a reducing catalyst for reducing divalent mercury (Hg2+) contained in the gaseous medium to metal mercury (Hg0), a gas-liquid separator for removing a moisture component contained in the gaseous medium, a dehumidifier equipped with a drain pump, an interfering component removal column for removing an interfering component such as, for example, sulfuric dioxide, and a mercury measuring instrument for measuring the concentration of metal mercury (Hg0) that has passed through the reducing column. The reducing tube referred to above allows the metal mercury (Hg0), reduced from the divalent mercury (Hg2+), and the metal mercury (Hg0), initially contained in the gaseous medium, to pass therethrough.
With this measuring device, the divalent mercury (Hg2+), which could not be measured in the form as it stands, can be reduced to the metal mercury (Hg0) that can be measured and, therefore, the total quantity of mercury contained in the exhaust gases can be measured. See, for example, the Japanese Laid-open Patent Publication No. 2004-354067.
It has, however, been found that the conventional apparatus for measuring mercury of a type referred to above has the following problem. Specifically, since the reducing tube filled with the reducing catalyst is surrounded with and is therefore heated by a heating device such as, for example, a heater for the purpose of facilitating the functionality of the catalyst filled therein, stain such as snoot does not easily deposit, but is apt to deposit within an outlet port of the reducing tube, at which temperature decreases as compared with that at upper and intermediate portions of the reducing tube, and within the gas-liquid separator. If the outlet port of the reducing tube and the gas-liquid separator are allowed to stand without the stain being removed, the mercury will be adsorbed in those portions thereof where stain deposited. Once this occurs, the adsorbed mercury will lead to a measurement error which would eventually lower the sensitivity of the measuring instrument for measuring the quantity of mercury contained in gaseous medium, with the reliability of the apparatus for measuring mercury lowered consequently.